1. Technical Field
The present invention relates to a light emitting device, a method for manufacturing the light emitting device, an electronic device provided with the light emitting device, and electronic equipment provided with the electronic device.
2. Related Art
Electroluminescent devices using organic semiconductor materials (hereinafter, simply referred to as an “organic EL device”) have been extensively developed in expectation of their use as solid-state luminescent devices or emitting devices for use in inexpensive large full-color displays.
In general, such an organic EL device has a structure in which a light emitting layer is provided between a cathode and an anode. When an electric field is applied between the cathode and the anode, electrons are injected into the light emitting layer from the cathode side, and holes are injected into the light emitting layer from the anode side.
At this time, in the case where a molecular structure of organic EL materials (light emitting layer materials) is a specific structure or an aggregation state of molecules of the organic EL materials is a specific state, the injected electrons can not be combined with the holes immediately, and therefore the injected electrons and the holes are retained for a certain period of time in a specific excitation state.
Therefore, in such a specific excitation state, total energy of the molecules increases only for an amount of excitation energy as compared to a ground state which is a normal state. Pairs of the electrons and the holes which are being retained in such a specific excitation state are referred to as exciter (exciton).
After a lapse of the certain period of time, when the exciter disintegrates and thereby the electrons are combined with the holes, the increased excitation energy is released to the outside of the organic EL device as heat and/or light.
The light is released in the vicinity of the light emitting layer. A quantity of the released light based on the excitation energy is affected by the molecular structure of the organic EL materials or the aggregation state of the molecules of the organic EL materials significantly.
In such an organic EL device, it has been known that a layered device structure, in which an organic semiconductor layer formed of organic semiconductor materials having different carrier transport properties for carriers (electrons or holes) is provided between a light emitting layer and a cathode and/or an anode, is effective in obtaining high luminance.
In order to obtain high luminous efficiency in such an organic EL device having a structure in which a light emitting layer and an organic semiconductor layer (hereinafter, referred to as “organic semiconductor layers”) are provided between an anode and a cathode, extensive researches and studies are conducted on molecular structures of organic EL materials and organic semiconductor materials to be used, aggregation states of molecules of these materials, a number of the organic semiconductor layers, a laminated position thereof, and the like.
However, even in the organic EL devices modified as described above, characteristics such as luminous efficiency and the like are not so improved as to meet expectations in actuality (see JP-A H09-255774, for example).
Recently, the reason why such sufficient characteristics improvement cannot be obtained has been roughly known. Namely, in such organic EL devices, interaction between a constituent material of each electrode (metal material) and an organic semiconductor material of an organic semiconductor layer adjacent to the electrode is larger than interaction between the organic semiconductor materials of the adjacent organic semiconductor layers.
Therefore, sufficient adhesion cannot be obtained between the organic semiconductor layer and each electrode, so that transfer of the carriers is not carried out smoothly between the organic semiconductor layer and the electrode.